TBC == Truck Body Control - aka. Body Control module. The TBC fuse powers the Body Control Module (BCM), Remote Control Door Lock Receiver, and Multifunction Switch Flash to Pass featuer all on CKT 1140 (circuit 1140).
Have you measured the amp draw on the circuit? Does the blinking persist if you test at the TBC fuse instead of at the battery? How about when you disconnect the BCM or RKE module? The BCM is located just right of center under the dash. It will have 3 connectors plugged into the left side of the module.
I did a search for 'TBC' and 'swartlkk' as the author and came up with THIS THREAD
and THIS THREAD
which doesn't precisely match your problem, but could provide useful information.